Method of reducing quartz crystal activity



Sept. 7, 1937. B. CLARK I 2,092,049

METHOD OF REDUCING QUARTZ CRYSTAL ACTIVITY Filed March 28, 1936 lll flll l l WITNESSES: INVENTOR 85a ,I' Bernarc/L, C/a/K ATTO NEY PatentedSept. 7, 1937 PATENT OFFICE METHOD OF REDUCING QUARTZ CRYSTAL ACTIVITYBernard L. Clark, Medfield, Mass., assignor to Westinghouse Electric &Manufacturing Com- Dany, East Pittsburgh,

Pennsylvania Pal, a. corporation of Application March 28, 1936, SerialNo. 71,440

5 Claims. (01. 250-36) My invention relates to improvements in radiocircuits, and more particularly in improving the operation of a tubecircuit embodying as an element thereof a crystal for stabilizing thefrequency of its operation.

In operating circuits wherein crystals are employed for obtainingfrequency stability, care must be exercised to avoid overloading thecrystal, as this causes brushing of the crystal and quite often resultsin rupturing of the same. I

It is an object of my invention to provide a circuit involving crystalcontrol in which the crystal may be operated without overloading thesame.

Another object of my invention is to provide a circuit involving crystalcontrol wherein the safe loading of the crystal may be simply andconveniently adjusted for.

Additional objects of my invention will be disclosed in the followingdescription of the same taken in conjunction with the accompanyingdrawing wherein the single figure is a circuit diagram of a radiocircuit involving crystal control and embodying my invention.

In electron tube circuits wherein crystals are employed to maintainfrequency stability, it is customary in one type circuit, as illustratedin the figure, to connect a crystal l between or in circuit with a gridelectrode 3 and a cathode 5 and in shunt thereto, there is usuallyprovided a high impedance element 1, usually a high resistance tofunction as a grid leak whereby to obtain proper bias for the tube 9.The output circuit of such a discharge device usually comprises a tunedcircuit including a condenser H and an inductor 13, which tuned circuitis resonant at approximately the frequency of the crystal. A battery IEor other source of potential is connected in the circuit to supply theproper potential for the anode of the tube. This circuit, as justdescribed, comprises a source of frequency in that it will oscillate atthe frequency of the crystal. Duringoperation the energy fed backthrough the crystal from the output circuit by way of the grid platecapacity within the tube, is apt to reach such proportions as to causebrushing of the crystal and possible rupture.

One way of reducing this loading on the crystal would be to lower thevalue of the grid leak impedance, but to do so would be to alter thebias developed on the tube and correspondingly produce a change in theoutput current. Satisfactory operation of the system would thereby beimpaired.

In order to bring the plate current back to the proper value, it wouldbe necessary to increase the grid leak impedance and thus return to thesame conditions as previously existed.

In applying my invention to a circuit of this type, I provide a path oflow impedance at radio frequencies between the cathode side of thecrystal and a point on the grid leak resistor. This low impedance pathat radio frequencies may economically comprise a condenser I 1 betweenthese two points, the proper point on the grid leak being determinedmost conveniently by making this connection adjustable and shifting italong the resistor until proper desired loading of the crystal isobtained.

The advantages which I attribute to my im-,

proved circuit, reside in the fact that while I am enabled to veryconveniently adjust the loading on the crystal, I can accomplish thiswithout interfering with the biasing of thetube, and consequentlywithout in any way destroying the proper operation of the system as awhole. The normal plate current is maintained irrespective of theadjustment of the loading on the crystal. Furthermore, should one desireto alter the value of the grid leak for any desirable reason, this canbe accomplished without readjusting the loading on the crystal by merelyadding some resistance in series with the grid leak, or if theresistance of the entire leak be changed, the proper loading on thecrystal can still be conveniently adjusted to proper operating value.

While I have disclosed my invention as applied to a specific circuit,the principle thereof is applicable to other circuits involving the useof crystals, and I do notdesire to be limited in my protection to thespecific disclosure set forth in my drawing, except as may benecessitated by the prior art.

I claim as my invention:

1. In combination, an electron discharge device having a grid electrodeand a cathode, a crystal in circuit between said grid and cathode, agrid leak connected in circuit with saidgrid and cathode, means forproducing feedback energy into said crystal circuit sufficient tooverload said crystal, and means for providing a low impedance path atradio frequencies, between the cathode side of said crystal and a pointon said cient to overload said crystal, and means for providing anadjustable low impedance path at crystal frequency around said crystal,said path including a portion of said impedance.

3. In combination, an electron discharge device having a grid electrodeand a cathode, a crystal in circuit between said grid and cathode, animpedance connected in a separate circuit between said grid and cathode,means for feeding energy into said crystal sufiicient to overload thesame, and means for reducing the loading on said crystal comprising alow impedance path at radio frequencies, between the cathode side ofsaid crystal and a point on said impedance, the connection to saidimpedance being adjustable.

4. In combination, an electron discharge device having a grid electrodeand a cathode, a crystal connected between said grid and cathode, a gridleak connected in a separate circuit between said grid and cathode,means for normally overloading said crystal during operation, and meansfor shunting said crystal with a low impedance path at radiofrequencies, said path including a selectable portion of said grid leak.

5. In combination, an electron discharge device having a grid electrode,an anode and a cathode, a crystal in circuit between said grid andcathode, a grid leak connected in a separate circuit between said gridand cathode, a circuit resonant at approximately the frequency of saidcrystal, connected between said anode and cathode and comprising meansfor feeding energy into said crystal sufficient to overload saidcrystal, and means for shunting said crystal with a low impedance pathat radio frequencies, said path including a portion of said grid leak.

BERNARD L. CLARK.

